Magnetic suspension systems are well known in the art. Such systems can be divided into two basic classes: active bearings and passive bearings. Active bearings use electromagnets that are controlled by a closed loop control or servo mechanism. Such systems require means to measure the position of the supported body and means of regulating the electric current in the electromagnets. They are, therefore, complex and costly systems.
Passive bearings in general use the attractive and repulsive forces of electromagnets or, preferably, permanently magnetized materials to generate support forces. No servo control or positioning measuring means are required. The passive bearings currently in use, however, are limited to one axis of stability, while the axes orthogonal to the stable axis are generally unstable. For example, in a rotatable configuration a passive bearing can be configured to be stable radially, but is then unstable axially. Conversely the bearing could be configured to be stable axially, but is then unstable radially. Linear bearings have similar stability limits.
One method of addressing this limitation is to use a mechanical bearing or an active magnetic bearing to stabilize and provide load support in the non-stable axis. This introduces the limitations of the mechanical or active magnetic bearing into the systems, respectively.
Another known method of addressing this problem is to construct bearings from conically shaped magnets. The unstable axis in this configuration is parallel to the surface of the cone, while the stable axis is perpendicular to the surface. Mechanical stability can be achieved for a limited range of cone angles. Unfortunately it is difficult and costly to manufacture conical magnets with the high magnetic energy required to produce useful bearing forces.
Yet another method of addressing the shortcoming is to rely on gyroscopic or eddy current forces to achieve dynamic stability. These types of systems are unstable in one or more axis when at rest, but become stable when the system rotational speed exceeds a certain critical value. These systems require mechanical bearings and/or active magnetic bearings to stabilize and provide load support below the critical rotational speed. This again introduces the limitations of the mechanical or active magnetic bearing into the systems.